There are many sensors for measuring properties of fluids, and they vary widely in utility, sensitivity, ruggedness and reliability. It is a desirable objective to provide a rugged, simple and reliable sensor to respond to properties of fluids which are related to the opposition by the fluid to its own physical displacement. Examples of applications for such a sensor are determining the quality of a fluid, i.e., whether the fluid is all liquid, all gas or vapor, or some mixture of them. Such information can, in turn, be used for information alone, or to control a system to restore the quality to some desired value. An example of a system utilizing this information is a control for the level of oil supply in an internal combustion engine. There are, of course, other applications for sensor which utilize different displacement-resisting properties, for example viscosity, to determine some monitored condition of a fluid, for example the degree of dilution of oil by gasoline.
By sensing the opposition of a fluid to its own displacement, information can both be obtained and can be put to use to control systems which utilize the fluid for some other purpose. To this end, the sensor can also be used as a pump to cause the fluid to flow in the system for an advantageous purpose. One example of such an arrangement is the maintenance of a correct oil level in an internal combustion engine as discussed above. An additional advantage which can be secured is the incorporation of external oil reservoirs in the engine oil system which form part of the actively-used lubricant rather than merely a static reserve. This extends the period between oil changes and the addition of oil, and enlarges the protection of oil systems from excessive dilution by engine fuel. These are important advantages when the engine is in a remote location, or one which is difficult to reach. Improving the reliability of an engine, and decreasing the frequency of routine service visits, can make appreciable cost savings possible.
There are many other uses to which the type of information derived by a sensor according to this invention can be employed for control purposes. It must be said that the applications for sensors according to this invention can be fulfilled by other types of sensors, which may or may not use the same physical property. However, many of the most useful applications of this sensor are in circumstances where ruggedness, simplicity, compactness, and reliability are at a premium, and the sensor of this invention greatly excels many of the conventional sensors available as an alternate.
The range of possible fluid substances with which our invention may deal is limited generally to those which can be pumped or otherwise caused to flow in a fluid path or duct. Within this limitation we may deal with a broad range of possible fluids, which may consist of or contain gases or vapors, liquids, emulsions, mists and even suspended or entrained solids. Among fluids of the same composition we may find variations in physical condition such as of temperature, pressure, viscosity or vapor pressure, which it may be our purpose to identify. Variations in the state or quality of the fluid system which may affect opposition to fluid displacement may include differences in head or state of flow, or the presence or absence of a fluid at a particular point in the fluid system.